In a passenger vehicle it may be desirable for a display, such as a video display, to be hidden when not in use. A mechanical device is necessary for deploying and retracting the display. In most environments, the mechanical device may also be subject to additional constraints such as size, weight, and power constraints. In some environments there may be additional constraints. For example, in an aircraft environment a mechanical device used for deploying and retracting an overhead display must automatically retract in the event of power loss to the cabin, or in the event that the head of a passenger strikes the display.
Traditional methods for deploying and retracting displays in passenger vehicles include the use of linkage arms extending from a motor to a monitor to rotate the monitor to a pre-set viewing position. A slip clutch between the monitor and the motor allows for the display to retract when struck from a certain direction. A mechanical spring stores the energy for automatic retract of the monitor in an emergency situation resulting in the loss of power.
Displays have been deployed and retracted by mechanisms linking the motor to the monitor by gears. The gear and motor linkage approach wears at the pivot points and the monitor vibrates during transportation making viewing difficult. Vibrations in the display during transport may be reduced with tighter tolerance gears, but tighter tolerance gears would be ineffective from both weight and cost perspectives, and gear tolerance will be lost with time and use.
Vibrations in the display have also been reduced by using a brake and by driving a motor in reverse. The brake damps the vibrations transmitted to a display from a motor while the display is deploying, and maintains the display in a deployed position. The display is moved from the deployed to a retracted position by first releasing the brake. Vibrations are damped while the display is retracting by driving the motor in reverse. The energy necessary to move the display from the deployed to the retracted position is generally stored in a spring. Since driving the motor in reverse increases resistance to the movement of the display, a larger spring is required when this technique is used for damping vibrations. Often, larger springs create noisy whines when they are wound and unwound in this way.
In some passenger vehicles, the electromagnetic interference (“EMI”) generated by a display may also be an issue. Power and video distribution systems use single stranded wires or combinations of flex and single stranded wires to distribute power. The power is distributed between the video board in the monitor assembly and the main chassis. The length of the wires, and the high frequencies of the video signals being transmitted through them, together act like an antenna. In general, any mechanical device designed for deploying and retracting an overhead display must attempt to mitigate the effects of EMI on the video signal transmitted to the display.